In a reflector antenna[?], the relative reduction in the effective aperture of the antenna caused by the masking effect of other antenna parts, such as a feed horn or a secondary reflector, which parts obstruct the radiation path.
... is the skeletal muscle that allows voluntary control over urination.
In the human female, the urethra is about 1-1.5 inches (25-38 mm) long and opens in the vulva ...